1. Field of the Invention
This invention relates to amplifiers for translating low voltage clock signals to CMOS levels suitable for integrated circuit logic.
2. Description of Related Art
Crystal oscillator circuits generate clock signals in many applications. FIG. 1 shows an example of a crystal oscillator circuit 100. Oscillator circuit 100 contains a current source 110, a transistor 120, and a crystal 130. Transistor 120 has its gate and drain coupled to the terminals of crystal 130 to create a positive feedback loop. Crystal 130, commonly a quartz crystal, resonates at a characteristic frequency which generates a periodic signal Vin across transistor 120. In order to maintain low current consumption in the oscillator circuit 100, signal Vin has small voltage swings that are insufficient for operation of CMOS logic. Accordingly, an amplifier 160 is required to generate from signal Vin an output signal Vout which oscillates between maximum and minimum levels which are sufficient to switch N-channel and P-channel transistors in CMOS logic.
Since very low power applications such as electronic watches often employ oscillator circuits, amplifier 160 is often required to be power efficient. Power efficient operation becomes more difficult at higher frequencies because faster switching and/or greater amplification is required. Accordingly, efficient high frequency amplifiers are needed.